This invention relates generally to vacuum processing systems and more particularly to isolating the vacuum manifold in such systems.
Semiconductor devices, among other articles, are commonly fabricated by performing a series of process steps inside an airtight chamber maintained below atmospheric pressure. Systems for semiconductor fabrication typically comprise a mechanical pump for evacuating the process chamber via a vacuum manifold. The contents of the process chamber, which include residual particles and byproducts of the fabrication process, are pumped to a burn box for destruction. The process chamber is isolated from the mechanical pump and the vacuum manifold by a foreline valve. The foreline valve is in its open state during processing and is in its closed state during a majority of system maintenance tasks.
A throttle valve is located immediately downstream of the foreline valve to control the pressure in the process chamber. The throttle valve is connected to the vacuum manifold by a flexible hose, commonly referred to as the foreline flex hose. The flexible nature of the flex hose facilitates making the connection between the throttle valve and the vacuum manifold. Also, the flex hose is able to contract while the mechanical pump is operating, which reduces the stress on the other components of the system.
Such processing systems require a number of maintenance tasks, both scheduled and unscheduled. For instance, the throttle valve and flex hose need to be periodically removed for cleaning. Because the operations within the process chamber are typically carried out at temperatures significantly higher than room temperature, the byproducts exiting the process chamber are at a high temperature and tend to condense on the interior surfaces of the throttle valve and the flex hose, which are generally at room temperature. Buildup of these condensates can create restrictions; restrictions in the foreline can cause backpressure and a failure to pump down all of the residual particles.
Custom heated jackets made to fit over the throttle valve, and even the flex hose if desired, are available. By heating the components they enclose to the higher temperature of the processing chamber, such jackets are generally effective at preventing condensation where used. However, this means that condensate build-up is simply moved downstream of the jackets. Furthermore, use of such jackets results in increased energy costs and increased maintenance time for jacket removal.
To remove the flex hose and throttle valve for cleaning or other maintenance, a technician must shut down the mechanical pump, remove the flex hose, install a blank-off cap on the inlet of the vacuum manifold, and then restart the mechanical pump. This process has a number of drawbacks. First, it is a relatively lengthy process that leads to excessive downtime and greater maintenance costs. Second, in the case of dry mechanical pumps, this process increases the risk of pump seizure because such pumps are more likely to seize up while turned off. A seized pump requires the expense of replacing or rebuilding. Lastly, because unexpectedly high pressure in the foreline could cause byproducts to spew out of the flex hose as it is disconnected, the removal of the flex hose is when the maintenance technician is most likely to be exposed to potentially harmful byproducts.
Frequent service of the burn box is another maintenance task necessary with such processing systems. The mechanical pump is shut down during burn box maintenance, and the system is purged with nitrogen while the mechanical pump is not operating. Besides the risk of pump seizure associated with dry mechanical pumps, this procedure suffers from the additional problem that any residual particles not fully removed because of restrictions in the foreline will tend to migrate back to the process chamber during the nitrogen purge.
Accordingly, there is a need for a vacuum processing system that minimizes the need to shut down the mechanical pump during system maintenance, thereby increasing the life of the mechanical pump, avoids back streaming of particles, reduces maintenance cost and downtime so as to increase tool availability time, and reduces safety risks to maintenance technicians.